Oxygen monitoring device

ABSTRACT

A gas monitoring device for monitoring gas levels within a chamber is provided. The gas monitoring device includes a housing having a probe with a sensor disposed on the probe. The probe extends through the housing and into a chamber such that the sensor is within the chamber. The housing includes a first passageway disposed about the probe and second passageway disposed about the first passageway. During operation of the gas monitoring device, a temperature adjusting medium enters the second passageway through an inlet of the housing and then enters into the first passageway via the second passageway. As the temperature adjusting medium travels through the first passageway, the temperature adjusting medium adjusts the temperature of the probe. The temperature adjusting medium adjusts the temperature of the probe through thermal conduction. As the temperature of the probe adjusts, the temperature of the sensor also adjusts through thermal conduction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gas sensing devices. Morespecifically, the present invention relates to a gas sensing device formeasuring oxygen levels in fuel tanks.

2. Description of Related Art

Since 1959, a number of aircraft fuel tanks have unexpectedly exploded.Typically, the explosions occurred when an unknown ignition sourceignited the fuel/vapor mixture in the fuel tank. Fuel/vapor mixtures arecreated during consumption of fuel within the fuel tank by engines ofthe aircraft. The consumed fuel leaves a space within the tank whichgenerally fills with atmospheric air containing oxygen. The presence ofboth a flammable gas and the fuel/vapor mixture within the space createsthe potential for an explosion within the fuel tank upon ignition. Theindustry has responded with various methods and apparatuses, asdiscussed in Air Safety Week, Vol. 15 No. 16, Apr. 16, 2001, “FatalExplosion Highlights Hazard of Flammable Vapors in Fuel Tanks.”

One prior art method which reduces fuel/vapor combustion includes theelimination of combustible gases from the fuel tank. This prior artmethod fills space within a fuel tank with an inert gas. The presence ofthe inert gas within the fuel tank deprives the fuel/vapor mixture of aflammable gas necessary for combustion. Nonetheless, the need tocontinuously fill the fuel tank with an inert gas and the attendant highcosts associated therewith do not make this an attractive alternativefor aircraft manufacturers.

A more efficient method in accordance with the prior art includesflooding the tank with inert gas when oxygen levels become high. Thismethod requires continually measuring oxygen levels in a fuel tank. Thesensors must stay at a constant temperature level in order to accuratelymeasure oxygen levels. However, temperatures of fuel tanks in vehiclestend to fluctuate depending on the outside temperature. Therefore, theoxygen sensor's temperature must be kept at a constant level in order toallow accurate measurements by the oxygen sensor.

Prior art attempts to keep the temperature of a gas sensor constantinclude heating the gas sensor with electric resistance heaters when thetemperature is low. However, these methods are not suitable for use infuel tanks, as electrical current applied to the electrical resistanceheaters may potentially ignite the fuel/vapor mixture within the tank,again making this an unattractive option for aircraft manufacturers.

Therefore, a need exists for a method and apparatus which maintains atemperature of a gas sensor at a constant level. This new method andapparatus should minimize the introduction of elements which may ignitea fuel/vapor or other hazardous mixture within a fuel tank and/or space.

BRIEF SUMMARY OF THE INVENTION

The present invention fills the aforementioned needs by providing amethod and apparatus for maintaining a temperature of a gas sensingdevice which measures gas levels within a chamber which minimizes theintroduction of elements which may ignite a medium within the chamber.

In one embodiment of the present invention, a gas sensing device havinga housing, a probe and a passageway is disclosed. The housing includes afirst end and a second end where the second end has an inlet and anoutlet. The probe includes a fiber optic disposed within the housing anda sensor. The fiber optic extends through the housing such that an endof the fiber optic is adjacent the first end of the housing. The fiberoptic end includes the sensor which senses gas surrounding the sensor.The passageway of the gas sensing device, which is disposed about thefiber optic, is in fluid communication with both the inlet and theoutlet of the housing. The passageway conducts a temperature adjustingmedium from the inlet to the passageway. The temperature adjustingmedium adjusts a temperature of the probe and a temperature of thesensor through thermal conduction.

In another embodiment of the present invention, a method for maintaininga set temperature of a probe of a gas sensing device is disclosed. Theprobe of the gas sensing device extends through a passageway of ahousing of the gas sensing device and into a chamber. The passageway ofthe gas sensing device includes an inlet and an outlet. The methodcomprises conducting a temperature adjusting medium through thepassageway. The method also monitors a temperature of the probe duringconduction of the temperature adjusting medium. The method adjusts anamount of the temperature adjusting medium conducted through thepassageway in response to a monitored temperature of the probe where themonitored temperature differs from the set temperature of the probe. Inthis embodiment, adjusting the amount of the temperature adjustingmedium conducted through the passageway adjusts the temperature of theprobe through thermal conduction thereby maintaining the probe at theset temperature. Likewise, adjusting the amount of temperature adjustingmedium conducted through the passageway also adjusts a temperature of agas sensor disposed on an end of the probe through thermal conduction.

In a further embodiment of the present invention, an oxygen monitoringdevice is described. The oxygen monitoring device includes a housing, afirst passageway, a probe and a second passageway. The housing includesa first end and a second end where the second end has an inlet and anoutlet. The first passageway, which is disposed within the housing, isin fluid communication with the outlet of the housing second end. Theprobe is disposed within the first passageway and extends through thefirst passageway and beyond the housing at the housing first end.Furthermore, the probe includes a fiber optic having an end extendingbeyond the housing and a sensor. The sensor, which is disposed on thefiber optic end outside the housing, senses gas surrounding the sensor.The second passageway of the oxygen monitoring device is disposed aboutthe first passageway. The second passageway is in fluid communicationwith both the inlet and the first passageway such that the secondpassageway conducts a temperature adjusting medium from the inlet to thefirst passageway for adjusting a temperature of the probe. When thetemperature adjusting medium adjusts the temperature of the probe, thetemperature of the sensor is also adjusts through thermal conductionwith the probe.

As may be appreciated, the present invention provides a method andapparatus for maintaining a temperature of a gas sensor within a chamberwhile minimizing the introductions of elements which may combustflammable material located within the chamber.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 illustrates a side view of a gas sensing device partiallydisposed within a chamber in accordance with an embodiment of thepresent invention.

FIG. 2 is a side view of a gas sensing device having an enclosure inaccordance with an embodiment of the present invention.

FIG. 3 illustrates the gas sensing device shown with reference to FIG. 1with a shield disposed thereon in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a gas sensing device for sensing gaslevels within a chamber. The gas sensing device includes a housing and aprobe disposed within the housing having a tip extending from thehousing into the chamber. The probe tip includes a gas sensor disposedthereon for sensing gas levels within the chamber. As will be discussedin greater detail with respect to the accompanying Figures, duringoperation, the gas sensing device maintains a temperature of the gassensor via passageways disposed around the probe within the housing ofthe gas sensing device.

Now making reference to the Figures, and more particularly FIG. 1, FIG.1 illustrates a side view of a gas sensing device 100 partially disposedwithin a chamber 160 in accordance with an embodiment of the presentinvention. The gas sensing device 100 includes a housing 102, a probe112 extending through the housing 102 and a sensor 114 disposed at anend 112 b of the probe 112. The gas sensing device 100 also includes afirst passageway 106 disposed about the probe 112 and a secondpassageway 108 disposed about the first passageway 106. A vacuum layer104 surrounds the second passageway 108 thereby minimizing thermallosses of the gas sensing device 100. The gas sensing device 100 alsoincludes an insulation layer 103 which encapsulates the gas sensingdevice 100. In this embodiment of the present invention, the insulationlayer 103 may be vacuum chamber.

The housing 102 encloses the probe 112 and both the first and secondpassageways 106 and 108. The first and second passageways 106 and 108communicate with one another via passages 136, as may be seen withreference to FIG. 1. The first passageway 106 fluidly communicates withan outlet 122 and the second passageway 108 fluidly communicates with aninlet 120. During operation of the gas sensing device 100, a temperatureadjusting medium enters the gas sensing device 100 through an inlet 120at an end 102 b of the housing 102 and into the second passageway 108.After the temperature adjusting medium enters the second passageway 108,the temperature adjusting medium travels as indicated by directionalarrows X₁. The temperature adjusting medium then enters into the firstpassageway 106 through the passages 136. Once the temperature adjustingmedium enters the first passageway 106, the temperature adjusting mediumcontacts the probe 112 as it travels in a direction indicated bydirectional arrows X₃ towards the outlet 122, thereby adjusting atemperature of the probe 112 through thermal conduction. When thetemperature of the probe 112 adjusts, the temperature of the sensor 114also adjusts through thermal conduction. As may be seen with referenceto FIG. 1, a controller 135 provides the temperature adjusting medium tothe gas sensing device 100 in response to inputs received from the gassensing device 100.

The controller 135 receives inputs from temperature sensors such asthermocouples 110 a and 110 b mounted within the gas sensing device 100.The thermocouple 110 a mounts on the probe 112 within the firstpassageway 106, as shown with reference to FIG. 1. The thermocouple 110b mounts on the sensor 114 within the chamber 160. The thermocouples 110a and 110 b may be any thermocouple suitable for monitoring temperaturesof in-situ probes and gas sensors, such as platinum RTD, J-Kthermocouple or other temperature sensors and thermocouples known in theart.

During operation of the gas sensing device 100, the thermocouples 110 aand 110 b provide data to the controller 135 which may be used toascertain the temperature of the sensor 114 and the probe 112 as morefully discussed with reference to commonly owned application Ser. No.09/994,714 filed on Nov. 28, 2001, the specification of which is hereinincorporated by reference in its entirety. Using the data acquired fromthe thermocouples 110 a and 110 b, the controller 135 adjusts the amountof temperature adjusting medium traveling into the gas sensing device100. To further illustrate, if data received by the controller 135 fromthe thermocouple 110 a indicates that the temperature of the sensor 114exceeds an optimal operating temperature of the sensor 114, thecontroller 135 reduces an amount of temperature adjusting mediumentering the gas sensing device 100. According to an embodiment of thepresent invention, when the controller 135 reduces the amount oftemperature adjusting medium entering the gas sensing device 100, thetemperature of the sensor 114 and probe 112 decreases. Furthermore, inaccordance with an embodiment of the present invention, the temperatureadjusting medium may be any medium capable of adjusting a temperature ofthe probe 112 and the sensor 114, such as air, a liquid or the like.

It should be noted that in the above-described example, the controller135 may also increase the amount of the temperature adjusting mediumtraveling into the gas sensing device 100 in order to increase thetemperature of the sensor 114. Moreover, in accordance with analternative embodiment of the present invention, a cooling temperatureadjusting medium may be used where the controller 135 reduces the amountof temperature adjusting medium entering the gas sensing device 100 inorder to increase the temperature of the sensor 114. Likewise in thisembodiment, the controller may increase the amount of temperatureadjusting medium entering the gas sensing device 100 in order to reducethe temperature of the probe 112 and the sensor 114.

It should also be noted that in a further embodiment of the presentinvention, the controller 135 may also adjust the temperature of thetemperature adjusting medium in response to the temperature of thesensor 114. For example, if the controller determines that thetemperature of the sensor 114 exceeds a predetermined value, thecontroller may decrease the temperature of the temperature adjustingmedium while holding constant the flow rate of the temperature adjustingmedium into the gas sensing device 100. Alternatively in thisembodiment, if the controller 135 determines that the temperature of thesensor 114 is below a predetermined value such as a set temperature, thecontroller 135 may increase the temperature of the temperature adjustingmedium while keeping constant the flow rate of the temperature adjustingmedium into the gas sensing device 100 constant thereby increasing thetemperature of the sensor 114.

The gas sensing device 100 monitors the presence of gas within thechamber 160 via the sensor 114. The chamber 160 may be any structurecapable of holding a medium, such as a fuel tank, a food storage bin orthe like. In an embodiment where the chamber 160 is an aircraft fueltank, the sensor 114 may be an optical device, such as an optical oxygensensor, capable of monitoring oxygen levels within the chamber while notintroducing electric current to the tank. In this embodiment, opticaloxygen sensors function by sending light through an optical fiber to athin coating such as hydrophobic sol-gel containing a ruthenium complex.The light from the optical fiber excites the ruthenium complex, therebycausing fluorescence. While in the sol-gel, if the excited rutheniumcomplex contacts an oxygen molecule, the flourescent signal is quenchedthereby preventing collection of light energy by the fiber optic.Therefore, the amount of energy collected by the fiber optic isproportionate to the number of oxygen molecules present in the sol-gel.The optical fiber collects the fluorescence light energy and carries thelight energy to a spectrometer. The spectrometer converts the lightenergy to digital data for oxygen level determination.

The amount of energy collected by the fiber optic is also proportionateto the temperature of the sol-gel. The temperature of the sol-geleffects the diffusion coefficient of oxygen in the sol-gel as well asthe frequency of collision in the sol-gel between oxygen molecules andthe excited ruthenium complex. Therefore, the temperature of the sol-gelmust remain constant to ensure accurate readings of oxygen levels withinthe fuel tank. An example of a sensor which may used as the sensor 114includes a Foxy Fiber Optic Oxygen Sensor available from Ocean Optics,Inc. located in Dunedin, Fla.

In an embodiment where the sensor 114 is an optical sensor, the probe112 includes fiber optics 124 a and 124 b which couple with aspectrometer 130, as may be seen with reference to FIG. 1. Duringoperation, the fiber optics 124 a and 124 b monitor the presence ofoxygen within the chamber 160 via the sensor 114. The fiber optics 124 aand 124 b send information gathered by the sensor 114 to thespectrometer 130 for oxygen level determination within the chamber 160.

The gas sensing device 100 interfaces with the chamber 160 with acompression fitting 116. The compression fitting 116 may be any devicesuitable for interlocking the gas sensing device 100 with the chamber160 such as compression fittings available from Swagelok™ located inSolon, Ohio. In addition to the compression fitting 116, the gas sensingdevice 100 also includes interfaces 118. The interfaces 118 hold theprobe 112 as shown with respect to FIG. 1 such that as the temperatureadjusting medium travels through the first passageway 106, thetemperature adjusting medium surrounds the probe 112, thereby improvingthermal conduction between the temperature adjusting medium and theprobe 112.

Now turning attention to FIG. 2, FIG. 2 illustrates an alternativeembodiment of the gas sensing device 100 shown with reference to FIG. 1,where the gas sensing device 100 includes an enclosure 105. As may beseen with reference to FIG. 2, the enclosure 105 resides at a first end102 a of the housing 102 adjacent the sensor 114. The enclosure 105extends both the insulation layer 103 and the vacuum layer 104 such thatthe vacuum layer 104 extends around the end of the gas sensing device100 at first housing end 102 a, thereby increasing thermal stability ofthe gas sensing device 100. In addition, the enclosure 105 may seal anend of both the first and second passageways 106 and 108. Alternatively,the enclosure 105 may also extend the second passageway 108. It shouldbe noted that the gas sensing device 100 may be used for otherapplications including pharmaceutical, biomedical and food industryapplications where chambers having mediums requiring sterileenvironments are used.

Now making reference to FIG. 3, FIG. 3 illustrates the gas sensingdevice 100 shown with reference to FIG. 1 with a shield 132 inaccordance with an embodiment of the present invention. The shield 132may be compression fit onto the gas sensing device 100 using anysuitable technique. The shield 132 includes a shroud 142 disposedimmediately adjacent the sensor 114, as may be seen with reference tothe Figure. The shroud 142, which is held in place with struts 134,protects the sensor 114 from a medium disposed within the chamber 160during operation of the gas sensing device 100. In this embodiment ofthe present invention, the struts 134 are constructed from a gaspermeable material which permits passage of gases from the chamber 160into a volume 140 of the shroud 142. Gases monitored by the sensor 114travel through the shield 132 as indicated by directional arrow X₂ andinto the volume 140 for monitoring. Therefore, the struts 134 allowmonitoring by the sensor 114 of substances within the chamber 160. Anexample of a material which may be used for the construction of thestruts 134 is Gore-Tex™ available from W.L. Gore & Associates, Inc.located in Newark Del. It should be noted that during operation of thegas sensing device 100, should medium enter the volume 140, the shield132 includes passageways 138 which allow for passage of the medium fromthe volume 140 into the chamber 160.

The present invention provides an apparatus which may be used to monitorthe presence of oxygen in a fuel tank having a fuel/vapor mixture. Inaddition, the present invention provides a method and device formaintaining a temperature of a gas sensor at a constant level within afuel tank. The present invention maintains the temperature of a gassensing device within a fuel tank with a temperature adjusting medium,such as air. As such, the present invention minimizes the introductionof elements, such as electric current, which may cause combustion of afuel/vapor mixture within the fuel tank. Therefore, the presentinvention provides an attractive solution for monitoring gases withinchambers.

Moreover, the present invention provides a sensor which may be used tomonitor gases in a variety of applications. These applications include,but are not limited to, biomedical, pharmaceutical, food industry,heating, ventilating-air conditioning (HVAC) applications.

The above are exemplary modes of carrying out the invention and are notintended to be limiting. It will be apparent to those of ordinary skillin the art that modifications thereto can be made without departure fromthe spirit and scope of the invention as set forth in the accompanyingclaims.

1. A gas sensing device comprising: a housing having a first end and asecond end, the second end having an inlet and an outlet; a probe, theprobe including: a fiber optic disposed within the housing, the fiberoptic extending through the housing such that an end of the fiber opticis adjacent the first end of the housing; and a sensor disposed on anend of the fiber optic for sensing gas surrounding the sensor; apassageway disposed about the fiber optic, the passageway being in fluidcommunication with both the outlet and the inlet for conducting atemperature adjusting medium from the inlet to the passageway foradjusting a temperature of the probe.
 2. The gas sensing device of claim1, further comprising; a second passageway disposed about the firstpassageway, the second passageway being in fluid communication with thefirst passageway and the inlet.
 3. The gas sensing device of claim 1,wherein the probe extends beyond the first end of the housing.
 4. Thegas sensing device of claim 1, the housing further comprising: aninsulation layer surrounding the passageway.
 5. The gas sensing deviceof claim 4, the housing further comprising: vacuum layer.
 6. The gassensing device of claim 1, the gas sensing device further comprising: athermocouple disposed on the fiber optic end.
 7. The gas sensing deviceof claim 1, wherein the temperature adjusting medium is air.
 8. The gassensing device of claim 1, wherein the temperature adjusting medium is aliquid.
 9. The gas sensing device of claim 5, wherein the housing firstend further includes a enclosure which encloses the housing first endwhere the enclosure further extends the insulation layer about thehousing first end.
 10. The gas sensing device of claim 9 wherein theenclosure further extends the vacuum layer about the housing first end.11. The gas sensing device of claim 1, wherein the sensor is a geldisposed on an end of the fiber optic.
 12. A method for maintaining aset temperature of a probe of a gas sensing device, the probe extendingthrough a passageway of a housing of the gas sensing device and into achamber, the passageway including an inlet and an outlet, the methodcomprising: conducting a temperature adjusting medium through thepassageway; monitoring a temperature of the probe; adjusting an amountof the temperature adjusting medium conducted through the passageway inresponse to a monitored temperature of the probe where the monitoredtemperature differs from the set temperature of the probe, whereinadjusting the amount of the temperature adjusting medium conductedthrough the passageway adjusts the temperature of the probe throughthermal conduction thereby maintaining the probe at the set temperature.13. A method for maintaining a set temperature of a probe of a gassensing device as recited in claim 12, wherein the temperature adjustingmedium is air.
 14. A method for maintaining a set temperature of a probeof a gas sensing device as recited in claim 12, wherein the probefurther includes a sensor disposed at an end of the probe where thesensor is in thermal communication with the probe.
 15. A method formaintaining a set temperature of a probe of a gas sensing device asrecited in claim 14, wherein the probe further includes a fiber optic.16. A method for maintaining a set temperature of a probe of a gassensing device as recited in claim 15, wherein the sensor is a coatingdisposed on an end of the fiber optic.
 17. A method for maintaining aset temperature of a probe of a gas sensing device as recited in claim16, wherein the operation of monitoring a temperature of the probefurther includes monitoring a temperature of the sensor.
 18. A methodfor maintaining a set temperature of a probe of a gas sensing device asrecited in claim 17, the method further comprising: adjusting atemperature of the temperature adjusting medium in response to amonitored temperature of the probe where the monitored temperaturediffers from the set temperature of the probe, wherein adjusting thetemperature of the temperature adjusting medium adjusts the temperatureof the probe through thermal conduction and a temperature of the sensorthrough thermal conduction thereby maintaining both the probe and thesensor at the set temperature.
 19. An oxygen monitoring devicecomprising: a housing having a first end and a second end, the secondend including an inlet and an outlet; a first passageway disposed withinthe housing, the first passageway being in fluid communication with theoutlet of the housing second end; a probe disposed within the firstpassageway where the probe extends through the first passageway andbeyond the housing at the housing first end, the probe including: afiber optic having an end extending beyond the housing; and a sensordisposed on the fiber optic end outside the housing for sensing gassurrounding the sensor, the sensor being in thermal communication withthe probe; a second passageway disposed about the first passageway, thesecond passageway being in fluid communication with both the inlet andthe first passageway for conducting a temperature adjusting medium fromthe inlet to the first passageway for adjusting a temperature of boththe probe and the sensor via thermal conduction.
 20. The oxygenmonitoring device of claim 19, wherein the temperature adjusting mediumis air.
 21. The oxygen monitoring device of claim 19, wherein the sensoris a gel disposed on a tip of the fiber optic.
 22. The oxygen monitoringdevice of claim 19, the housing further comprising: an insulation layersurrounding the second passageway.
 23. The oxygen monitoring device ofclaim 19, further comprising: a thermocouple disposed on the fiber opticend.